I have a huge arsenal of Roombas. I think the count is up to 3 400 series Roombas, 1 500 series Roomba, 1 Dirt Dog and 2 Scoobas. I love having lots of these robots to clean and vacuum my house and houses that I sell too. As a result, I’ve gone through a LOT of batteries. What I’ve started to do is write dates on the battery of when I purchase them. If there is anything else special or substantial(such as used or li-ion) about the battery, I’ll write that on it too.

Looking to gain more run time and a longer cell life, I’ve tried out several Lithium Ion battery packs. If you’ve shopped for these, you’ll know that they are substantially more expensive than the plain NiMH batteries. I’m here to tell you that they are NOT worth the extra money. If I could buy a Lithium Ion pack for a 400 series Discovery for the same price as a NiMH, I might do that but otherwise I would advise against it. There are specifics for each robot as to why they are not well suited for use with a Lithium Ion pack. I will detail that below but the long and short of it is that the Roomba charging circuits are NOT designed to optimally charge a Lithium Ion pack. Most of the time the cells are being charged to 4.3v or maybe even higher. If you drop the peak charging voltage down to 4.2v, you gain substantially more charge/discharge cycles. I would say 4.2v versus 4.3v would result in a 100% increase in charge/discharge cycles.

The other problem is protection circuitry. Most(all?) of the Lithium Ion packs commercially available for the Roombas and Scooba do not have separate balancing/charging circuit boards. They all rely on “protected” cells. The protected cells have a circuit built in to protect them from catastrophic over charging and/or over discharging. These protection circuits are set at the absolute upper and lower limits of the cell’s operational ranges. They are set to protect against explosion and cell instability, not for cell longevity. Here are more specific problems present in each of the iRobot platforms:

500 series - The charging circuit is very touchy and is expecting specific characteristics. If those aren’t met, you will likely get an “error 5″ on the screen. Much more likely than you would with a NiMH pack. The internal charger also will consistently charge this pack over-voltage. It’s supposed to be 22.5v on the input side but mine puts out 22.97v even in circuit. I’m taking a wild guess that mine is not the only one that has this problem. By the time you trace the voltage to the battery pack, it calculates out to over 4.3v per cell which is too high.

400 series – The 400 series is probably the best candidate for a lithium-ion battery pack but still not necessarily a good one. Most vendors who sell these lithium-ion packs are relying on an internal cell protection circuit and the Roomba’s over discharge circuit to shut the pack down. Neither of these circuits are actually designed for that purpose. The Roomba’s circuitry is adjusted to optimally discharge NiMH packs and the internal cell protection is worst yet. That is ONLY a last resort and should never be relied on to repetitively be used for that purpose. If the cells somehow become out of balance, this can start happening a lot. The symptom is that the Roomba won’t park or go to a red light, it will simply die in the middle of the floor and become entirely lifeless. The power button won’t do anything until you charge it enough to be recognized. Another problem with the 400 series is that the Li-Ion pack makes the Roomba much lighter and it seems to have a harder time making contact on the dock without the added weight holding it down.

Scooba – This one is one of the worse of all. Personally I have a BAD habit of not taking the battery out right away when the Scooba dies. While I was fixing a Scooba for a friend one time, I was probing around trying to diagnose a problem and found that even when the Scooba is TOTALLY off, it’s still drawing quite a bit of power. I tested the output leg on the 78XX series regulator and found voltage there and a few other places. The logic was all still hot and drawing power as well. The power switch on the Scooba is essentially soft power. This is probably the case with the Roomba too although I haven’t tested it. The difference being the Scooba isn’t designed to dock. Not only that, I’ve always charged the battery out of the unit in the Scooba Charging Base. This is an extra step that I sometimes don’t have time for. As a result, I’ll sometimes forget about it entirely and the battery will sit in the Scooba and over discharge. Doing this a few times will surely fry a lithium ion pack and will eventually fry a NiMH even.

The bottom line is that you are far better off sticking with NiMH battery packs for the Roomba, Scooba and Dirt Dog. I have used the Tenergy Scooba Battery with success in the past although one of my friends has had VERY mixed results with the Tenergy rechargeable AA’s. For the Roomba, they have OEM Roomba batteries at the Renton, WA Frys for $40 which is a steal for a local store in my opinion since the list price is $69.99 or they have them on Amazon even cheaper at this link: iRobot 4905 Battery. For the 500 series, I have had success with this Aftermarket 500 series APS Battery sold by Allergy by Gone. If iRobot products were designed specifically for Li-Ion chemistry, I have no doubt that Li-Ion packs would perform fantastically and we would all benefit from longer run times and cell life but since they are not, I don’t think it’s a great idea to run these types of battery packs in your robots.

You may want to update your information because I have a lithium battery in my roomba right now, and it indeed has cell balancing technology built right into the pack. I bought it from http://www.lithiumpowerinc.com for $80. They told me in an email that they are working on one for the Scooba line as well.

Though it’s not a good idea in your opinion, thousands of people are using Lithium batteries in everything ROBOTIC lawn mowers to ROBOTIC gutter cleaners
The lithium battery in my Roomba is going strong like new.

It’s just not fair that a google search for “scooba lithium” brings up your page first.

Just because it was your opinion in 2010 that Lithium batteries are “not a good idea” doesn’t mean things don’t change.

You should test a pack out for yourself, or take this page down. It’s not fair to those who sell an excellent product (with 2 year warranty).

I have a roomba, if I charge it then unplug it and leave it for a week, the battery has been drained. The roomba does seem to use power while off. I looked into Lithium but a complete discharge of a lithium batter will be very hard on its longevity. Until iRobot makes a roomba that specifically designed with lithium in mind, I’ll be sticking to NiMH despite it reaching it’s half life in 2.5 years.

I have many many roomba. Most are dead. I have stop using scooba the 500s 600s. I now have 3 770s and 780. All were NimH. I have made many many battery packs trying to improve on OEM packs. Tenergy I had high hopes for. I have stop making packs due to poor cell rating and short life span.
Using LiIon on 770 and 780 for about 6 months. Cleaning schedule are each day so my roomba see a lot of charge dis-charge cycles. So far LiIon and the charging circuits have held up.

The problem is that the roomba has no internal cell balancing circuitry to deal with lithium cells. Many of the packs designed have no balancing circuitry either and simply rely on the over and under voltage protection circuitry to keep the battery in good health. That’s like driving your car around and using the redline cutoff as your shift indicator and then still exepecting to get 100,000 trouble free miles. The Tenergy cells have been a real mixed bag for me. Some good and some bad. Glad to hear you are having good luck with your lithiums right now. Did you build them or buy them? Did you add in a cell balancer?

Which one did you buy and from where? I’m sure people that stumble onto my blog would be interested as would I. I bought several Lipos and they were all terrible but I believe they did not have balancer boards built in. I think the theory was to use built in cell protection circuitry to do the job which is just totally unacceptable.

I purchased it from Roomba Exchange. I don’t think they’ve been made for years. I can no longer find them. At least I still have one that works great and hopefully will for at least a few more years. Unfortunately Li-Ion batteries don’t last much beyond 400 or 500 cycles before they go down hill fast.

BTW, you couldn’t just use Li-Ion batteries in place of NiMh batteries without some sort of circuit that converts the constant charge current to the pulse type needed by Li-Ion. It wouldn’t work and would be very dangerous. So yea, don’t just swap one type of battery for another. Li-Ion requires very specific charging algorithms that constantly monitor the charge rate, temperature and backoff on the pulse charging as the batteries charge rises.

What a load of doublespeak. It’s sad because this is one of the first results that Google shows.

The iRobot NiMH battery packs do not have individual cell taps either. So there is no “protection circuitry” for the NiMH packs that’s worth a damn, and I can attest to that after having one nearly catch fire in an iRobot fast charger. Given that finding end-of-charge is already screwed up for the NiMH chemistry for just 1 cell, putting, what, 12 cells in series without any taps works about as well as you would expect — i.e. it doesn’t. That’s why the NiMH packs die so quickly.

Furthermore, there are multiple lithium battery types. You don’t seem to be aware of this. The LiFePO4 cells are much more robust, easier to charge, and have better energy/power density. Usually the packs don’t go out of balance until end-of-life anyways, and they’re way more difficult to blow up so the taps are a little overkill anyways. The RC guys have been beating the crap out of these cells for, wow nearly 8-9 years now. Even at the time of writing, this article was still 4-5 years behind the times.

The charging circuitry needs to be change, but the charging lithium batteries is way easier than looking for some screwy delta-peak-whatever on NiMH cells. Some people have been zip-charging LiFePO4′s for hundreds if not more than 1000 cycles. It’s an easy change.

It’s ridiculous for iRobot to continue selling NiMH packs. To the point where the Roomba is more like an overcomplicated scheme for spurring the sales of NiMH batteries.

I wrote this blog post to prevent people from buying the lousy lithium batteries that I saw offered for about $150 for the Roomba 400 series at the time. I went through about 3 of them before giving up on them. Not to say that there are not better packs available now. Looking around now I see many choices for less than half of what I spent but I’m still a bit wary of them.

I agree with you entirely, it is pitiful that iRobot does not use lithium batteries in their vacuums. I have a set of Makita cordless tools with lithium packs and they are phenomenal. The difference though is that they are bundled with a charger that can properly deal with the cell chemistry and structure.

In my opinion, Roombas’ built in charger is very primitive and not suitable for charging a pack of lithium cells that are strewn together in series. You make a great point that it’s hardly even suitable for charging the NiMH packs. The Makita packs have a breakout header that goes to a balancing battery charger which I still feel is the best way to do it. I have a couple of RC plane and car packs. They also use balancing chargers. Not to mention the Shorai lithium-iron battery in my motorcycle which also uses a balancing charger.

I disagree that multiple charging taps are overkill. I’m all for anything that can make my battery last longer and adds a margin of safety. It’s not like balancing controller chips are all that expensive. Trusting individual cell protection to protect against an out of balance situation still seems like a bad idea.

You mention the RC guys beating the crap out of LiFePO4 packs… Yes, those are great packs and would serve nicely in a Roomba but I am not aware of any of those without balanced charger breakouts. If guys are charging those with NiMH chargers and getting away with it, more power to them. But why?

The battery is not the only place iRobot cheaps out on though. These vacuums are built like toys. While they are putting lithium batteries in our Roombas, I’d urge them to consider brushless motors and metal gears. A few minor changes would easily make these Roombas worth the $300-$600 they are charging for them.